Superheterodyne receiving circuit



Aug. 26, 1941.

V J. HAANTJES- EI'AL SUPERHETERODYNE RECEIVING CIRCUIT Filed Jan. l8, 1941 Fly.

Fr/ar Ari g cos w t C I Ep cos (a t INVENTORS .10

4N. HAANT/ES BERIWAR DU-S 0. 7' lL'GL-W ATTORNEY Patented Aug. 26, 1941 UNITED STATES PATENT OFFICE Johan Haantjes and Bernardus Dominicus Hubertus Tellegen, Eindhoven, Netherlands Application January 18, 1941, Serial No. 374,986 In the Netherlands July 9, 1939 3 Claims.

Circuit arrangements for heterodyne reception are known, which utilise a diode as a mixing tube. In this case the diode is located in a closed circuit having an impedance, to which are supplied the incoming signals, a second impedance which has the oscillations of the oscillator supplied to it and a third impedance for the intermediatefrequency signal formed. 'In most cases this series-circuit includes, in addition, a resistance shunted by a smoothing condenser and serving to supply the diode with a certain biassing potential.

Such arrangements have various drawbacks.

They are highly liable to modulation hum, cross modulation and howling tones, the latter especially in the case of incoming signals, whose frequency is simply related to, the intermediate fre quency, for example the double of it.

The extent, to which these drawbacks will be experienced, depends on the shape of the diode characteristic curve, that is to say the steeper the curve the more appreciable they will be.

The present invention now consists in that the above-mentioned resistance is but partly bridged by a condenser.

On the one hand, this results in the diode characteristic being rendered less steep. On the other hand, the circuit shows the property of the three above-mentioned interfering phenomena being rendered smaller with an increase of the oscillator voltage, at least as long as this voltage is considerably larger than that of the incoming signal, which is, however, practically always the case.

By achoice of a suitably high oscillator voltage, it is thus possible to make the circuit to satisfy very high requirements as regards modulation hum, cross modulation and howling tones.

The invention will be more clearly understood by reference to the accompanying drawing, given by way of example, in which Fig. 1 shows a diagram of a known diode-mixing arrangement.

Fig. 2 shows one example of an improved arrangement according to the invention.

The arrangement according to Fig. 1 is constituted by a diode D in series with a resistance R0, which is bridged by a smoothing condenser C. Further, there are series-connected a source of local oscillations Ep cos o t, the primary winding of a tuned intermediate-frequency transformer M and a source of voltage E1 cos wit brought about by the incoming high-frequency in Fig. 2 is substantially R is not bridged. The incoming signal picked up by the antenna A is fed inductively to the tuned input circuit S having the frequency mi. The input circuit is connected on one side to the anode of the diode D and on the other side to a circuit I which is tuned to an intermediate frequency mm. The diode cathode has connected to it seriesconnected resistances R and R0, only the latter being shunted by a condenser C. Local oscillations from source L of frequency Ep cos wpt are applied through transformer T, the secondary of which is'connected between resistance R0 and the intermediate frequency circuit I.

Good results with this arrangement are obtained at the following values:

Ep:25 volts elf.

Internal resistance of diode: about 10009 What we claim is:

1. In a mixing circuit, a diode rectifier, a resistance connected to the cathode of the rectifier, a condenser shunting only a portion of said resistance, and the series connection between the rectifier anode and said cathode resistance of a pair of tuned circuits and a local source of oscillations, one of the tuned circuits being resonant to the frequency of the incoming signal oscillations and the other of said circuits being resonant to an intermediate frequency resulting from mixing or" the local oscillations with the signal oscillations.

2. In a mixing circuit, a diode rectifier, a pair of series-connected resistances connected to the cathode of the rectifier, a condenser shunting only one of said resistances, and the series connection between the rectifier anode and said cathode resistances of a pair of tuned circuits and a local source of oscillations, one of the tuned circuits being resonant to the frequency of the incoming signal oscillations and the other of said circuits being resonant to an intermediate frequency resulting from mixing of the local oscillations with the signal oscillations.

3. In a mixing circuit as defined in claim 2, wherein the value of one of the cathode resistances is several times the value of the other, and the condenser is shunted across the resistance 01 larger value.

J OHAN HAANTJES. BERNARDUS D. H. .TEILEGEN. 

